Metal oxide catalysts containing iron, antimony and phosphorus are known to be useful in production of aldehydes by oxidation of organic compounds, production of dienes, alkenylbenzenes, unsaturated aldehydes or unsaturated acids by oxidative dehydrogenation of organic compounds, and production of nitriles by ammoxidation of organic compounds. For example, ammoxidation of propylene is described in JP-B-38-19111 (the term "JP-B" as used herein refers to an "examined Japanese patent publication"), and U.S. Pat. Nos. 3,542,843, 3,591,620 and 3,988,359; and ammoxidation of methanol is described in JP-B-54-39839 and U.S. Pat. No. 4,511,548.
The antimony-containing oxide catalysts which can be used in the reactions stated above involve problems, such as poor reproducibility and operability in the preparation thereof and difficulty in assuring high strength. As a result, some improvements have been made on a process for preparing the catalyst as described in JP-B-46-3456 and JP-B-46-3457, and U.S. Pat. Nos. 3,341,471, 3,657,155 and 3,686,138.
These conventionally proposed processes, however, do not always satisfy both activity and physical properties of the catalyst, and the problem of reproducibility of preparation still remains unsolved. In particular, in the preparation of catalysts having a high phosphorus content as in the catalyst of the present invention, direct application of conventional processes proposed for preparing antimony-containing catalysts fails to attain satisfactory results. For instance, the processes disclosed in U.S. Pat. Nos. 3,657,155 and 3,686,138 are excellent techniques for preparing iron-antimony-containing catalysts suitable for a fluidized bed process. However, it is difficult for these processes to produce catalysts containing a relatively large amount of phosphorus while retaining activity and physical properties for use in a fluidized bed process. This is assumed to be because the presence of a large amount of a phosphorus component not only inhibits oxidation of the antimony but greatly changes the properties of the slurry reducing its stability.
In addition, the above-cited two processes are limited in terms of the antimony compound which can be used as a raw material and conditions for preparing the catalyst. In more detail, according to the process of U.S. Pat. No. 3,657,155, use of a trivalent antimony compound as an antimony component is essential; the slurry containing this particular antimony compound should further contain ferric ion and nitrate ion; and the slurry should be adjusted to a pH of about 7 or less and heat-treated at a temperature of from about 40.degree. to 150.degree. C. prior to spray drying. Although the process of U.S. Pat. No. 3,686,138 does not require the co-presence of ferric ion and nitrate ion in the slurry containing an antimony compound, it essentially requires use of a pentavalent antimony compound as an antimony compound; and in a similar manner to the process of U.S. Pat. No. 3,657,155, the slurry before spray drying should be adjusted to a pH of about 7 or less and heat-treated at a temperature of from about 40.degree. to 150.degree. C. at that pH.